1. Technical Field
The present invention relates to a filter medium and the method of fabricating the same, and more particularly, to a composite filter medium and the method of fabricating the same.
2. Description of Related Art
Various designs of air cleaner have been proposed to improve the quality of life of human beings. Every technical development contributes to the significant improvement of the indoor air quality (IAQ). Generally, the air cleaners can be divided into several categories by the cleaning technology: the high efficiency particulate air filter (HEPA filter), the ultra low penetration air filter (ULPA filter), the activated carbon air filter, or the anion air filter, etc.
HEPA or ULPA filters are examples of the most popular filters used in the area of air cleaner. Commercially, the most commonly seen HEPA or ULPA filter include a paper product formed by combining glass fibers with resin. The paper product is fabricated by a wet process, in which the fibers (e.g., borosilicate glass fibers or cellulose fibers) are dissolved into a slurry containing water-soluble adhesives so that the fibers can be randomly directed, resulting in a better filtration efficiency. However, for an HEPA filter or a ULPA filter to achieve a satisfactory filtration effect, the weight per unit area thereof should be greater than 70 g/m2 (tested with 0.3 μm particulates under a flow rate of 10.5 L/min, the filtration efficiency being greater than 99.97%, the pressure loss being 32 mmH2O), which usually results in high pressure loss. Further, with regard to the glass fibers, there are problems arising from the high density, high air resistance, poor alkali resistance, brittleness, high melting point, and dermal irritation. Also, it is difficult to treat the waste by combustion, and thus the recycling becomes an issue.